Engine Control Cable Failure Forces Emergency Return to Carlisle

Casualties unknown • Incident with an aircraft ot the model Saab 340 near Carlisle Airport (UK), SE

A Saab 340B experienced a loss of propeller RPM control during climb, leading to an engine shutdown and emergency landing.

What happened

On 30 August 2019, a Saab 340B, registration ES-NSD, was performing a scheduled passenger flight from Carlisle Airport to London Southend Airport. During the climb, at an altitude of approximately 2,500 feet, the pilot noticed that the propeller RPM on the left engine was low. When the pilot attempted to adjust the engine power via the condition lever, the control failed to respond.

Following established procedures, the crew declared an emergency and initiated a shutdown of the left engine. The aircraft returned to Carlisle Airport and landed safely twelve minutes after departure. There were no injuries to the 13 passengers or 3 crew members on board, and no damage was reported to the aircraft.

The investigation

The investigation focused on the mechanical failure of the engine control system. Post-flight inspections of the left engine revealed significant damage to the condition control cable, specifically the section running between the hydromechanical unit (HMU) and the pitch control unit (PCU).

Investigators examined the installation of chafing protection on the cable. While a section of plastic tubing had been fitted to the cable, it was found to be in the incorrect position. Furthermore, maintenance records did not confirm that the recommended service bulletin for chafing protection (SB 340-76-027) had been officially implemented on this aircraft. The manufacturer also identified a discrepancy between the Powerplant Build-up Manual and the Aircraft Maintenance Manual regarding the specific requirements for bending the cables during installation.

Findings

  • The left engine condition control cable suffered damage due to chafing against the accessory gearbox.
  • Although chafing protection was present on the cable, it was not positioned correctly to prevent contact with the gearbox.
  • The failure of the condition lever to respond was directly linked to the degradation of the cable's outer casing and internal components caused by this friction.

Safety action

  • The aircraft operator has implemented a periodic inspection of engine control cables within its maintenance program.
  • The aircraft manufacturer has committed to updating the Aircraft Maintenance Manual (AMM) to include detailed guidance on correct cable installation and bending procedures to prevent premature wear.

Probable cause

The engine control cable failed because it chafed against the accessory gearbox, as the installed protective tubing was not positioned at the correct location to intercept the contact point.

Frequently asked questions

What happened in the 2019-08-30 aircraft accident near Incident with an aircraft ot the model Saab 340 near Carlisle Airport (UK), SE?

A Saab 340B experienced a loss of propeller RPM control during climb, leading to an engine shutdown and emergency landing.

What aircraft was involved and where did it happen?

The accident on 2019-08-30 involved a aircraft, at Incident with an aircraft ot the model Saab 340 near Carlisle Airport (UK), SE.

What was the probable cause of the accident?

The engine control cable failed because it chafed against the accessory gearbox, as the installed protective tubing was not positioned at the correct location to intercept the contact point.

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